In most silver halide photographic materials, except those of lith film and the like, both excellent gradation and wide exposure latitude are required.
In general, the sensitivity of a silver halide emulsion is known to depend on the size of the grains contained in the emulsion. Accordingly, the exposure latitude of a silver halide photographic material depends largely on the grain size distribution of the silver halide grains contained therein, and it is well known that it is possible to widen the exposure latitude by broadening the grain size distribution.
However, the presence of a mixture of silver halide grains of different sizes in the same layer has a disadvantage in that such is responsible for variation of development processing characteristics. This is because there is a great difference in the developing speed between silver halide emulsion grains having a large size and those having a small size when the silver halide emulsion undergoes development processing.
In an integral multilayer color photosensitive material it is particularly important to maintain the balance of the developing speeds among the constituent layers. Thus, the use of an emulsion which has a broad grain size distribution is undesirable from the view point of designing the photosensitive material.
In order to overcome the disadvantage arising from differences in the grain size, desensitizers have been added to emulsions, as described in West German Pat. No. 2,708,466 (corresponding to U.S. Pat. No. 4,301,242). However, this method is undesirable because it is accompanied by a decrease in the efficiency of using the silver and a deterioration of the granularity of the developed image.
It is also known that wide exposure latitude and soft gradation can be achieved by coating a spectrally sensitized high-speed emulsion and a spectrally sensitized slow emulsion in separate layers. However, multilayer coating is undesirable because the production thereof is complicated.
Moreover, there are known variable contrast photosensitive materials of the kind which can change their gradation depending on the wavelength range of the exposure light by mixing silver halides having different spectral sensitivities. However, it is difficult to stably acquire soft gradation with respect to the exposure wavelength range.